Detecting Patterns of Changes in River Water Temperature in Poland

Abstract

The study determined water temperature trends of rivers in Poland in the period 1971–2015, and also their spatial and temporal patterns. The analysis covered daily water temperature of 53 rivers recorded at 94 water gauge stations and air temperature at 43 meteorological stations. Average monthly, annual, seasonal and maximum annual tendencies of temperature change were calculated using the Mann–Kendall (M–K) test. Regional patterns of water temperature change were determined on the basis of Ward’s hierarchical grouping for 16 correlation coefficients of average annual water temperature in successive 30-year sub-periods of the multi-annual period of 1971–2015. Moreover, regularities in monthly temperature trends in the annual cycle were identified using 12 monthly values obtained from the M–K Z test. The majority of average annual air and water temperature series demonstrate statistically significant positive trends. In three seasons: spring, summer and autumn, upward tendencies of temperature were detected at 70%–90% of the investigated water gauges. In 82% of the analysed rivers, similarity to the tendencies of change of monthly air temperature was concluded, with the climatic factor being recognised as of decisive importance for the changes in water thermal characteristics of the majority of rivers in Poland. In the winter months, positive trends of temperature were considerably weaker and in general statistically insignificant. On a regional scale, rivers with a quasi-natural thermal regime experienced temperature increases from April to November. In the other cases, different directions of change in river water temperature (RWT) were attributed to various forms of human impact. It was also found that for the majority of rivers the average annual water temperature in the analysed 30-year sub-periods displayed upward trends, statistically significant or close to the significance threshold. Stronger trends were observed in the periods after 1980, while a different nature of water temperature change was detected only in a couple of mountainous rivers or rivers transformed by human impact. In the beginning of the analysed period (1971–2015), the average annual water temperature of these rivers displayed positive and statistically significant trends, while after 1980 the trends were negative. The detected regularities and spatial patterns of water temperature change in rivers with a quasi-natural regime revealed a strong influence of climate on the modification of their thermal regime features. Rivers characterised by a clearly different nature of temperature change, both in terms of the direction of the tendencies observed and their statistical significance, were distinguished by alterations of water thermal characteristics caused by human activity. The results obtained may be useful in optimising the management of aquatic ecosystems, for which water temperature is a significant indicator of the ongoing environmental changes.

Estimation of the Dependence of Ice Phenomena Trends on Air and Water Temperature in River

“…The majority of authors have focused on an assessment of change tendencies at the start and end dates of RI and its duration, which, in light of the recorded increase in TA and TW, usually gives a result pointing to the shortening thereof. Apart from warmer winters, an increase in TA in the autumn and spring periods has also been noticeable, especially during the last twenty years of the 20th century but in recent decades as well [38,39,[69][70][71][72], which delays the date of appearance of IP in rivers and also accelerates their disappearance. Analyses conducted for the last five-to-six decades in Polish rivers [21,22,24,25,31,42,51,64,65,[73][74][75] have confirmed that the duration of IP has been shortened, though their respective change trends have differed along individual river sections.…”

“…An analysis of circulatory determinants impacting the occurrence of IC in the Noteć River was performed by Graf and Tomczyk [23], while an assessment of the relationship between the TW of Polish rivers and large-scale atmospheric circulation, which was accompanied by the disclosure of TW change patterns in Poland, was carried out by Graf and Wrzesiński [38,39] and Marszelewski and Pius [71,72]. Research conducted by Yoo and D'Odorico [5] in Northern Europe showed that the ice regime of surface waters is connected with changes in the North Atlantic Oscillation (NAO) index, the features of which confirm long-term climate change [16].…”

“…The results of studies have pointed to the complexity of processes determining the thermal regime of rivers and confirm the impact of additional factors, regional and local, on their temporal and spatial variability. Spatial differences between thermal regime features are typical of rivers with a marked seasonality of supply in the temperate climate [39,59,71,72]. At the same time, no single trend attained statistical significance at the level of individual decades, which may have been due to either of two reasons: obviously, trends for decades were analyzed on the basis of a smaller quantity of data, which automatically translated into lower strength, or the observed growth trend may have been unclear over short periods of time in comparison with random fluctuations.…”

“…When assessing the role of the climate in controlling change trends in RI, research has been conducted on many scales and using various approaches, which has broadened the comprehensive analysis of time series and spatial trends regarding IP phenology and their connections with climate pattern trends. In the case of large spatial patterns of atmospheric circulation, emphasis has been placed on determining and indicating those systems that control regional air temperature fluctuations [34][35][36][37][38][39], but the empirical dependencies between dates of occurrence of ice on rivers and TA indices may not be reliable under future climatic conditions. Certain RI effects are strongly controlled by processes occurring on the scale of the catchment area and the river bed (e.g., the dynamics and intensification of river ice breakage fronts), which must be taken into consideration in the analyses of local factors.…”

The influence of treated wastewater from the Lodz city agglomeration on the ice regime and water temperature of the Ner river

“…In the last 70 years, sewage water discharged to the Ner has changed, both quantitatively and qualitatively. This was due to various processes and phenomena associated with the increase in population of the entire Lodz agglomeration, its economic and industrial development, changes in local water management, and river water temperature changes due to the warming climate (Graf, & Wrzesiński 2020). All of these caused long-term fluctuations and periodic trends in the quantity of sewage discharged into the river from the Lodz agglomeration, as well as similar changes in the degree of its biochemical, chemical and thermal pollution (only since 1995 has this wastewater been biologically treated in CWTP LA).…”